This invention relates to a system for quantitatively evaluating and characterizing imaging devices. The invention comprises an electro-optical system and a data analysis technique for the quantitative characterization of generated image and enables the comparison of such measurements with established standards of resolution and image quality. The necessity for a rapid, accurate means of characterize imaging systems arose from a request to objectively evaluate the image quality of U.S. Army night vision goggles (NVG) suspected in contributing to certain helicopter accidents. The field evaluated prototype of this effort is referred to as the "NVG Resolution Augmentation (NVGRA) to the AN/3895 TS".
The present method of resolution evaluation of U.S. Army night vision goggles (NVG) relies on an imprecise subjective pass/fail judgment by a trained observer viewing a test pattern through the NVG. The resolution of NVG is presently determined by examining a series of carefully designed patterns which vary in fineness of detail. For the purpose of this application only the reticle (test pattern) used in the latest revision of the AN/3895 Test Set (TS) will be considered. The reticle viewed by the NVG under this test includes two horizontal sets of numbered gratings 72 millimeters apart, consisting of:
(1) Group 2, Element 6 through Group 3 Element 5 of the U.S. Air Force 1951 Resolution Target for high light level testing.
(2) Group 1, Element 4 through Group 2 Element 3 of the U.S. Air Force 1951 Resolution Target for low light level testing.
Between the two horizontal sequences of six targets is a black rectangular box whose two sides subtend a field measuring one by six degrees. Centered in this rectangular box is a small circular hole whose diameter subtends six minutes. These targets are centered in the 40 degree field of view of test set. The present procedure requires a trained technican to clearly resolve a designated rating in each of two set of targets when viewed at the proper light level for a given model of the NVG. Determining which of the targets is clearly resolved is subjective and, consequently, imprecise.